Effect Of The Lode Parameter In Predicting Shear Cracking Of 2024-T351 Aluminum Alloy Taylor Rods

Recent investigations have shown that the ductility of a metal may depend on not only the stress triaxiality but also the Lode parameter, especially in the relatively low stress triaxiality range. However, applications using the Lode dependent fracture criterion are few and the value of incorporating the Lode parameter into a fracture criterion to predict impact related fracture is poorly understood. In the present paper, Taylor impact test by using 2024-T351 aluminum alloy rods of 5.95 mm diameter and 29.75 mm length was firstly conducted in a one-stage gas gun in the impact velocity range of 110.8–312.7 m/s. Mushrooming and shear cracking were observed in the test with increasing impact velocity. Subsequently, mechanical tests were conducted in a universal testing machine and a SHPB test facility. By using a hybrid experiment–numerical method, a modified version of Johnson–Cook strength model, a Lode-dependent fracture criterion as well as the Johnson–Cook (JC) fracture criterion were calibrated. Finally, 3D FE model corresponding to the test was built in ABAQUS and then was adopted to predict the shear cracking of the Taylor rods. It was found that FE simulations by using the Lode dependent fracture criterion give reasonable fracture pattern predictions while that using the Johnson–Cook fracture model obviously underestimates the fracture behavior. Detailed analysis shows that the dominant stress state of the material in the projectile\u27s fracture region in the impact event is in the range where the Lode parameter has an obvious influence on the metal\u27s ductility. FE simulations by using virtual metals also show that the Taylor impact fracture behavior prediction is much dependent on the effect of the Lode parameter on a material\u27s ductility

Revisiting the two-side optimization problem in satellite pursuit-evasion

In the present paper two-side optimization problem where the intercepting satellite pursuits the target satellite was studied. In the pursuit-evasion game the continuous thruster and the simple central gravity with J2 perturbation were involved for two satellites. With applying the functional extremum condition, the optimal control outputs of both side satellites were obtained by building the systems Hamilton function. Further, the two side optimal problem was transformed to the TPBVP, which contributed the solution with the mixed numerical method. Finally, the proposed method was validated by the numerical simulation, where the optimal interception and escaping trajectories were illustrated

Revisiting the two-side optimization problem in satellite pursuit-evasion

In the present paper two-side optimization problem where the intercepting satellite pursuits the target satellite was studied. In the pursuit-evasion game the continuous thruster and the simple central gravity with J2 perturbation were involved for two satellites. With applying the functional extremum condition, the optimal control outputs of both side satellites were obtained by building the systems Hamilton function. Further, the two side optimal problem was transformed to the TPBVP, which contributed the solution with the mixed numerical method. Finally, the proposed method was validated by the numerical simulation, where the optimal interception and escaping trajectories were illustrated

NUMERICAL MODELING OF THE VIBRATIONAL POPULATION DISTRIBUTION OF POLYATOMIC MOLECULES EXCITED BY IR LASERS

A computing model is presented for the calculation of the transient population distribution of polyatomic molecules excited by an IR laser pulse, SF8 has been used as an example. This model allows the calculation of the vibrational energy distribution from the observe IR fluorescence or adsorption spectrum, and vice versa. The thermal vibrational distribution calculated by this model the measured spectrum of SF6 at 300 K is in good agreement with the Boltzmann distribution (Table 1). The present model has a few advantages over an earlier study((1)), such as higher precision of computation, accurate generation of the vibrational transition matrix and being capable of calculating the transient vibrational population distribution at any instant after laser excitation. Using the model as rotationally resolved spectrum of SF6 at 20K has been obtained for the first time

Revising the Observation Satellite Scheduling Problem Based on Deep Reinforcement Learning

Earth observation satellite task scheduling research plays a key role in space-based remote sensing services. An effective task scheduling strategy can maximize the utilization of satellite resources and obtain larger objective observation profits. In this paper, inspired by the success of deep reinforcement learning in optimization domains, the deep deterministic policy gradient algorithm is adopted to solve a time-continuous satellite task scheduling problem. Moreover, an improved graph-based minimum clique partition algorithm is proposed for preprocessing in the task clustering phase by considering the maximum task priority and the minimum observation slewing angle under constraint conditions. Experimental simulation results demonstrate that the deep reinforcement learning-based task scheduling method is feasible and performs much better than traditional metaheuristic optimization algorithms, especially in large-scale problems

Two-Dimensional Self-Assembly of Linear Molecular Rods at the Liquid/Solid Interface?

We report on the synthesis and scanning tunneling microscopy (STM) studies of a series of linear molecular rods (1−5) comprising different numbers and/or spatial arrangements of perfluorinated benzene and benzene subunits interlinked with diacetylenes in the para position and decorated with or without terminal dodecyl chains. The molecules organize themselves into well-ordered 2D crystal structures at the liquid/solid interface through intermolecular and molecule−substrate interactions. Whereas the molecules substituted by dodecyl chains form the lamellar structures with alternating rigid core rows and alkyl chain rows, the unsubstituted ones change the orientation of the rigid backbones with respect to the lamellar axis. The molecular arrangement is not influenced by fluoro substituents on any phenyl ring of the backbone, which suggests that the interactions between the π-conjugated backbones are dominated by close packing rather than by the dipole moments of the rods or fluorine-based intermolecular interactions

A GA-SA Hybrid Planning Algorithm Combined with Improved Clustering for LEO Observation Satellite Missions

This paper presents a space mission planning tool, which was developed for LEO (Low Earth Orbit) observation satellites. The tool is focused on a two-phase planning strategy with clustering preprocessing and mission planning, where an improved clustering algorithm is applied, and a hybrid algorithm that combines the genetic algorithm with the simulated annealing algorithm (GA–SA) is given and discussed. Experimental simulation studies demonstrate that the GA–SA algorithm with the improved clique partition algorithm based on the graph theory model exhibits higher fitness value and better optimization performance and reliability than the GA or SA algorithms alone

Investigation of Acoustic Properties on Wideband Sound-Absorber Composed of Hollow Perforated Spherical Structure with Extended Tubes and Porous Materials

Traditional porous media such as melamine foam absorb sound due to their three-dimensional porous struts. However, the acoustic properties at low frequencies are greatly related to its thickness. In this paper, a novel type of thin and lightweight sound absorber composed of melamine foam and hollow perforated spherical structure with extended tubes (HPSET) is introduced to enhance the sound absorption performance at low frequencies. A theoretical model for the normal absorption coefficient of the HPSET with melamine foam is established. Good agreements are observed between the simulated and the experimental results. Compared with the virgin melamine foam, the proposed absorber can greatly improve the low-frequency sound absorption and retain the mid- to high-frequency sound absorption, while the thickness of the proposed absorber is less than 1/28 of the wavelength

High-Speed Micro-Particle Motion Monitoring Based on Continuous Single-Frame Multi-Exposure Technology

The impact phenomena of solid micro-particles have gathered increasing interest across a wide range of fields, including space debris protection and cold-spray additive manufacturing of large, complicated structures. Effective motion monitoring is essential to understanding the impact behaviors of micro-particles. Consequently, a convenient and efficient micro-particle motion monitoring solution is proposed based on continuous single-frame multiple-exposure imaging technology. This method adopts a camera with excellent low-light performance coupled with high-frequency light-emitting diode (LED) flashes to generate short interval illumination. This technology can, in theory, achieve 1 million effective frames per second (fps) and monitor particles as small as 10 microns with speeds up to 12 km/s. The capabilities of the proposed method were validated by a series of micro-particle motion monitoring experiments with different particles sizes and materials under varying camera configurations. The study provides a feasible and economical solution for the velocity measurement and motion monitoring of high-speed micro-particles